The manipulation of chemical and/or biological materials in a laboratory environment has become increasingly automated in order to increase the throughput of the analyses executed by the equipment, to reduce the costs of manual labor in the laboratory, to increase the reliability of the analyses, and to reduce the exposure of laboratory workers to contact with hazardous chemical and/or biological materials. As a result, robotic arms have been incorporated into instruments to transport objects during the conduct of experiments in order to support the higher throughput and unattended processing time for the experiments. A common step in many of these experiments involves fluid manipulation such as pipetting, diluting, dispensing and aspirating of fluids. A device commonly used for the performance of fluid manipulation in an automated system is a multi-channel pipetter.
A typical pipette tip is formed with a substantially conical head and a frustoconical body. The tip head, which mates with the pipetter head, forms an opening at its proximal end while the body forms a smaller opening at its distal end. The pipette tip head has a larger outer diameter than the pipette tip body and forms an annular lower edge at the junction of the head to the body. In use, the head of the pipette tip is typically force fit onto the shaft of another device, such as a pipetter, and held in place by friction. The pipetter is operated to draw liquid into and to expel liquid from the pipette tip through the distal opening in the tip body.
In general, automated instruments utilizing multi-channel pipettors use replaceable tips to minimize the probability of carry-over and contamination while transferring compounds, proteins, DNA, RNA, cells, blood and other fluids between microtiter plates. Thus, during the conduct of experiments, pipette tips are repeatedly placed on pipettors and used to aspirate and to dispense liquids. Typically, the pipette tips are placed on a pipette tip head of an automated pipetter instrument and inserted into a number of wells of industry standard multi-well plates. The robotic pipetter instrument positions the pipette tips into the wells of the plate, and liquid is aspirated from the wells and into the pipette tips. Alternatively, liquid is dispensed from the pipette tips and into the wells. As a result, pipette tips are normally sold packaged in flats or racks which hold the tips in a standard arrangement for placement on pipette tip heads and insertion into the wells of multi-well plates.
For example, two common pipette tip arrangements include 96 or 384 pipette tips. Typically, the pipette tip heads are inserted into a number of apertures of a pipette tip holding card with the positioning of the pipette tips and apertures chosen to be compatible with a standard 96 or 384 multi-well plate. For example, the standard 96 aperture pipette tip rack and flat has a rectangular upper surface that defines an 8×12 array of 96 receptacles with approximately 9 millimeters separating the centers of adjacent receptacle apertures. Each aperture of the card has a diameter larger than the outer diameter of the pipette tip body, but smaller than the diameter of the annular lower edge of the pipette tip head. To store a pipette tip in the rack or flat, the body of the pipette tip is inserted into one of the receptacles, and the annular lower edge of the pipette tip engages the upper surface of the rack or flat. The pipette tip then rests within the receptacle with the head of the tip extending above the upper surface of the rack or flat and the body of the tip extending below the upper surface.
One of the most error-prone steps in automated pipetter instruments occurs during attachment of the pipette tips onto the head of the multi-channel pipetter. For example, a malfunction of an automated system incorporating a multichannel pipetter results when a tip holding card of a pipette tip flat remains attached to some or all of the pipette tips after attachment to a pipetter head. The malfunction may result when even a minor misalignment between any one of the pipette tips and the pipetter head occurs, or when the pipette tip flat includes any defectively manufactured tip or is itself defectively manufactured. The resulting malfunction can result in a failure to transfer fluid and may lead to a robot crash requiring human intervention and jeopardizing the original intent of unattended operation. Tight manufacturing tolerances for the pipette tips and pipette flats have not sufficiently resolved the problem. Therefore, what is needed is a tip loading assembly having increased tip loading reliability and reduced failure modes. This and other benefits are provided by the present invention as described herein below.